High-data-rate communications as defined in the WiMAX IEEE 802.16-2004 standard may pave the way for true broadband, multimedia services over wireless networks. Based on orthogonal-frequency-division-multiplex (OFDM) techniques, the WiMAX physical-layer (PHY) and media-access-control (MAC) protocols are outlined in the IEEE 802.16-2004 standard.
In a WiMAX receiver, it is necessary to estimate the noise power and the received signal strength indicator (RSSI). The noise and RSSI estimators are needed in the Carrier-to-interference-plus-noise ratio (CINR) calculation. The noise estimation is necessary since the preamble symbols are boosted compared to the data symbols and, thus the total received power estimator cannot use directly in CINR calculation.
Received-signal-strength-indication (RSSI) estimation provides a simple indication of how strong a received signal is at a receiver front end. If the received signal strength is stronger than a predefined threshold value, then the link can be considered to be good. Compared to other measurements like CINR and block error rate (BER), RSSI estimation is simple and computationally less complex, as it does not require any processing and demodulation of the received samples. However, the received signal includes noise, interference, and other channel impairments. Therefore, receiving a good signal strength does not tell much about the channel and the signal quality. Instead, it gives an indication whether a strong signal is present or not in the channel of interest. CINR estimation can be employed by estimating signal power and interference power separately and then by taking the ratio of these two. The channel parameter estimates can be used to calculate the signal power.